In construction machinery, such as excavator loaders, group transmissions are used in the practice which need at least two actuated switching elements per gear. These group transmissions are either synchromesh gears (also known as synchro-shuttle gears) having hydraulically actuatable switching elements for travel direction only, or powershift or full-throttle powershift gears, the design of which has, in addition to switching elements for selection of travel direction, switching elements with which other reduction ratios can be adjusted, for example, in forward drive.
The control blocks used for controlling said gear designs differ mainly in that the synchromesh gears need a special idling valve, for reasons of safety, by means of which, depending on certain limiting conditions in the vehicle or in the transmission, but independently of the momentary state thereof, an idling speed can be adjusted. To control powershift gears, on the contrary, the gear control system needs its own shifting valve, by means of which it is possible to switch between several gear steps for traveling under load.
Different control blocks with different shift valves and switching elements are thus disadvantageously required for said gear design.
Due to the non-uniform constructional design of the gear control systems high manufacturing costs for the individual shift valves and switching elements, result because of the quantity of parts.